But community campaigners, backed by psychiatrists and a warning from the World Health Organization, have long believed that one of the active ingredients, cathonine, can lead to mental problems among regular users and have called for Britain to join much of the developed world by banning the drug.

Some of the most vocal critics of the drug have emerged recently from within the Somali community here. Khat, they say, is not only bringing harm to individuals, but it's also stymieing wider integration efforts.

"My people are in trouble because of this drug and I tell you ... London hasn't seen the worst of it," says Abdi Hussein, a young Somali migrant and former addict.

Thus far, Britain's Home Office has parried arguments for controlling khat, saying it is a mild narcotic and an innocent cultural past time with few proven social or medical ills.

'Khat has slowly been killing our community'

Each week, according to a widely cited but likely outdated government estimate, around seven tons of the leafy stimulant arrives at Heathrow Airport from the khat fields of Ethiopia and Kenya, to be whisked to khat cafes, known as mafreshis, frequented by many of Britain's 250,000-strong Somali migrant community, as well as the country's smaller Ethiopian and Yemeni groups.

Chewers devour up to two pounds of the leaf in a session. Similar to the chewing of cocoa leaves among Andean people, khat use is a centuries-old tradition originating in East Africa and the Arabian peninsula.

It has a social function of lubricating political debate and religious study – early users reportedly included Koran scholars – as well as quelling hunger in a poor corner of the world. In a Western context, the role of khat is less clear. A growing clamor of voices favor a ban amid concerns that the drug is wreaking havoc in Britain's large Somali population.

"Khat has slowly been killing our community but no one has paid any attention, until now," says former khat addict Abukar Awali. At the height of his habit, Mr. Awali says he chewed up to eight pounds of leaves daily.

"It's no exaggeration to say it is preventing us from integrating," he says. "When you chew, you don't work or meet anyone apart from Somalis. Maybe 80 percent of our men chew khat. When you are not chewing, you become paranoid and depressed. Everybody in my community knows someone with a khat problem; they are just afraid to say it."

While the debate over whether to control the drug continues, campaigners say its use is playing a role in alarming rates of unemployment, crime, and poor educational achievement among the country's Somalis.

The largest wave of Somali refugees arrived in Britain in 1991 after the collapse of Somalia's government and the onset of civil war. Already dislocated from their homeland, the majority were heaped into Britain's already overcrowded and poor inner-city estates.

With the newcomers came a more relaxed attitude toward khat. The drug has become more widely accepted now by the British Somali community.

"Khat is now seen as something from 'our' culture; an identifying point," says youth worker Hanad Mahamoud, from Brent, a London borough with at least 3,8000 Somali residents. "But that's nonsense. In Somalia, clan elders used to chew khat and talk politics. Here, men, women, and teenagers are chewing it all day just to get marqaan" – high – "on the bus, in the street, not working, not looking after themselves or their kids. They can't see that it is a part of 'culture' which has grown on the streets of Brent, not Mogadishu."

"It is at the heart of the dysfunctionality of the Somali community," Mr. Gardiner says. "It's a driver for crime, dropping out of school, and unemployment. It is also clearly a gateway to taking – and dealing – harder drugs. It is frankly rubbish to suggest it is innocent."

Is khat preventing British Somalis from thriving?

The government recently hinted that it may at last be listening to the warnings about khat.

The Advisory Council on the Misuse of Drugs, which helps shape Britain's drug laws, last month commissioned new research into the medical and social impacts of khat. The new report is expected to be released by the end of the year and the Home Office.

Last month, Home Secretary Jacqui Smith heard private testimony from a group of young Somalis whose lives have been blighted by khat. She was, by all accounts, moved by their stories of neglect and squandered opportunity.

Among those giving evidence was Mr. Hussein, the young Somali migrant who was able to kick his addiction.

"I used to think khat was a leaf, just like chewing grass – animal antics," he says with staccatoed urban eloquence.

"But it messed up my head. You're chilled when you chew, but the lows are very dark. Lots of my friends don't go to school because they are chewing all night. It started them into other drugs, but I got out in time."

Student Miski Abdullahi agrees, suggesting that khat has even dulled the entrepreneurial instincts of the community.

"Families are claiming state benefit and then spending it on khat, not their children. Somalis are doing well in the US and Canada, but are backward here. You have to ask 'why?' "

Concerned youngsters like Ms. Miski and Abdi campaign with the knowledge that they are fighting both the Home Office and the elders of their closely knit community, many of whom are reluctant to kick the khat habit or the lucrative businesses it has seeded.

The question of criminalizing Somalis also looms large, given the growing number of young Somalis falling into the criminal-justice system and the current negative connotations in Britain ascribed to being young, black, Muslim, and from a refugee community.

But campaigners say until khat is banned Somalis will struggle to find their place in Britain.

"They say 'the night which is darkest, is the night before dawn,' " explains youth worker Hanad Mahamoud, citing a Somali proverb. "Khat is a cancer killing my people, we will never integrate until it is gone."